Vehicle alcohol interlock systems appear to provide a useful technology for reducing the recidivism of suspended driving-while-intoxicated (DWI) offenders. These devices prevent the starting of the vehicle if the driver has a blood alcohol concentration (BAC) of .03 or higher. An extensive set of studies has demonstrated that interlocks are approximately 65% effective in reducing recidivism when installed on the vehicle of otherwise fully suspended DWI offenders. However, when given the option to install the interlock during a period when they would otherwise be fully suspended, only about 1 in 10 DWI offenders takes advantage of the opportunity to drive legally with the interlock. To increase offender motivation to install an interlock, some states are making it a requirement for reinstatement of the driver's license so that failure to install becomes a permanent barrier to driving legally. This application requests funds to extend a preliminary study of more than 82,000 DWI offenders who were convicted after the new law went into effect and sentenced to the Florida interlock program, which was among the first to adopt this procedure. Our preliminary study has indicated that making the interlock a prerequisite to reinstatement appears to increase the participation rate but delays implementation of the program. The study proposed in this R21 application will collect pre-law data in Florida to determine whether relative to the absence of such a law, requiring an interlock for reinstatement delays the reinstatement of all DWI offenders, users and nonusers, and whether it reduces overall statewide DWI recidivism. PUBLIC HEALTH RELEVANCE: Typically offered as an option for driving during part of the license suspension period, alcohol ignition interlocks have been shown to reduce the risk to the public of injury in a highway crash by substantially reducing the frequency of impaired driving by DWI offenders. This study will determine whether a new approach to interlocks-requiring DWI offenders to install them as a condition of driver's license reinstatement enhances the public health benefits of interlocks by increasing the number of offenders who install them and producing greater reductions in recidivism.